Thirsty (for knowledge) Thursday: Where Does Your Fat Go?

When you lose weight, where does your fat go? I've never really thought about this. I think I probably assumed that it exited via some obvious physical discharge like through poop (or maybe pee), but it's really something I never considered.

In a new study by Andrew Brown at the University of New South Wales and former physicist Ruben Meerman in the British Medical Journal, they say "there is surprising ignorance and confusion about the metabolic process of weight loss. The correct answer is that most of the mass is breathed out as carbon dioxide. It goes into thin air."

Whaaaaaaaaaaat? That wouldn't have been in my top 10 theories of where fat goes. Here's more:

Excess carbs and proteins are converted into chemical compounds called triglycerides (which consist of carbon, hydrogen, and oxygen) and then stored in the lipid droplets of fat cells. To lose weight, you’re attempting to metabolize those triglycerides, and that means unlocking the carbon that’s stored in your fat cells.

Losing 10 kilograms of human fat requires the inhalation of 29 kilograms of oxygen, producing 28 kilograms of carbon dioxide and 11 kilograms of water. That’s the metabolic fate of fat.

They calculated the proportion of the mass stored in those 10 kilograms of fat that exits as carbon dioxide and as water when we lose weight. Then, by tracing the pathway of those atoms out of the body, they discovered that 8.4 of those kilograms are exhaled as carbon dioxide. Turns out, our lungs are the primary excretory organ for weight loss. The remaining 1.6 kilograms becomes water, which is excreted in urine, feces, sweat, breath, and tears.

They also noted that their study doesn't mean that you can simply breathe more to loose weight. That just leads to hyperventilation, followed by dizziness, palpitations, and loss of consciousness. So stop huffing and puffing while you're sitting there. Just go for a run.

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